Green coffee beans of the same batch but roasted by different suppliers or shops tend to smell strikingly different or produce drinks of markedly different tastes. Obviously, the steps and equipment of “roasting” have certain effect on the flavor of the roasted beans and the drinks prepared therefrom. The existing roasting steps are briefly described below with reference to FIG. 1:
1. Bean selection: Before roasting the coffee beans C, it is necessary to pick out and remove therefrom all the beans that may have adverse effect on the resulting roasted beans (e.g., those partially eaten by insects).
2. Getting ready: The selected coffee beans C to be roasted are placed in a standby area 20, which is typically beside a roaster 10.
3. Bean feeding: Once the roasting cylinder 12 of the roaster 10 is preheated to the predetermined temperature, the selected coffee beans C in the standby area are poured into a hopper 11, through which the beans enter the roasting cylinder 12.
4. Heat absorption: The coffee beans C in the roasting cylinder 12 begin to absorb heat.
5. Ignition and heating: The person in charge of roasting turns on a gas burner switch 13 to heat the roasting cylinder 12. The heat of the burner and the extent to which an air valve 14 is opened can be adjusted according to roasting requirements.
6. Waiting for the first crack: The coffee beans C heated in the roasting cylinder 12 will undergo the first crack when the temperature in the roasting cylinder 12 reaches about 200° C. Before that, the person in charge of roasting can evaluate the degree of roast of the coffee beans C by means of a sample spoon 15 at the front of the roaster and, if necessary, finetune the gas burner switch 13 and the air valve 14 accordingly.
7. Opening the air valve 14 in a timely manner: Based on the roasting condition, the air valve 14 is opened to discharge the chaff, or better known as silver skin, of the green coffee beans. Overheated chaff generates an undesirable smoky smell and will compromise the flavor of the resulting coffee.
8. Bean discharge: The timing of discharging the roasted coffee beans is critical to the flavor, characteristics, and water content of the beans. The roasted coffee beans C are released onto a table in the cooling tank 16.
9. Cooling: The scalding coffee beans C are allowed to cool down on the table in the cooling tank 16.
10. Bean reselection: Beans that are broken during the roasting process are picked out and removed from the coffee beans C.
Each of the roasting steps described above may be performed differently from one roasted coffee bean supplier to another, depending on the preferences, knowledge, and experience of those who oversee the roasting process, and all such differences have direct or indirect effect on the flavor of coffee. As a matter of fact, however, the flavor of coffee generally known to or perceived by the public depends entirely on the degree of roast; that is to say, the timing of ignition, the heating temperature, and the heating duration directly determine the roasting result. In other words, the degree of roast has been viewed as the most important factor in the flavor of a cup of coffee.
According to the above, the quality of coffee as a drink hinges on the roasting process of coffee beans, And because of that, a variety of advanced coffee bean roasters have been imported to Taiwan from abroad (e.g., the United States, Germany, Italy, Spain, Turkey, Japan, Korea, and China). Many local companies have also dedicated themselves to the development and manufacture of coffee bean roasters. Take some common types of coffee bean roasters on the market for example. Each coffee bean roaster 30 in FIG. 2a, FIG. 2b, and FIG. 2c is provided with a hopper 31 and an internal receiving space 300, where a roasting cylinder 32 is installed. The roasting space (not shown) in each roasting cylinder 32 is in communication with the corresponding hopper 31 so that green coffee beans be fed into the roasting space through the corresponding hopper 31 in order to be heated and roasted. With continued reference to FIG. 2a, FIG. 2b, and FIG. 2c, the roasting cylinder 32 in each coffee bean roaster 30 is typically made of stainless steel or a cast iron alloy, and their heating methods can be respectively identified as half hot air/direct flame (FIG. 2a), direct flame (FIG. 2b), and hot air (FIG. 2c), depending on the way each heat source F1, F2, or F3 heats the corresponding roasting cylinder 32. The direct-flame heating method refers to heating a roasting cylinder 32 directly with the corresponding heat source, whereas the hot-air heating method refers to heating a roasting cylinder 32 through hot air generated by the corresponding heat source, i.e., indirectly. Regardless of the heating and roasting method employed, however, it is difficult for any of the coffee bean roasters 30 to keep coffee beans in the optimal heated or roasted state, and in consequence the roasted coffee beans are often heated unevenly. More specifically, the roasted coffee beans may be burned and carbonized on the outside but remain green inside, which phenomenon hinders the oil in the coffee beans from being released sufficiently and evenly, and hence from bringing out the optimal and most natural aroma and flavor of the beans, which is truly a shame.
While discussing the degree of roast, it is imperative to know what “roasting” is in relation to coffee beans. Roasting in this regard refers to heating and frying green coffee beans until the beans are charred on the surface to the desired degree. This description, however, is only superficial. The ultimate goal of roasting coffee beans is to maximize the characteristics of each kind of green coffee beans by finding out their unique degree of roast and stopping the frying or roasting process as soon as that degree is reached; only by doing so can the best drinking quality of each type of coffee be attained. Generally, the optimal degree of roast of each kind of coffee beans depends on the species of the beans and cannot be determined without repeated practice, inspection, and sampling. Nevertheless, all the commercially available coffee bean roasters 30 shown in FIG. 2a, FIG. 2b, and FIG. 2c use metal roasting cylinders 32 that are heated directly or indirectly to roast the coffee beans therein and that therefore may lead to a loss of oil, and hence of the best and most natural flavor, from beans that are dried out by the high temperature in the coffee bean roasters 30. Moreover, the high temperature of the coffee bean roaster 30 using the direct-flame roasting method is very likely to burn the green coffee beans being roasted. Should that happen, the oil in the coffee beans will be carbonized under the high temperature or even transformed into compounds that are harmful to the human body. This, too, is a major drawback of the conventional coffee bean roasters 30 and the existing roasting techniques.
It is an important issue for the coffee bean roaster industry, which is also the issue to be addressed by the present invention, to develop a roasting cylinder configured for a coffee bean roaster and capable of distributing the thermal energy in the coffee bean roaster precisely and evenly without increasing the power consumption or operation time of the coffee bean roaster, so as to rapidly and precisely produce roasted coffee beans whose natural aroma are well preserved and which are free of the bitterness of burning or carbonization, allowing consumers to enjoy affordable, high-quality, and healthy coffee.